Silex nowadays means a finely ground processed nearly pure "silica" or "silicates" which are used as pigments in paints. The first known use occurs circa 1590 as a post-medieval/Early Modern Era term in Latin for (presumably) powdered or ground up "Flints" (i.e. stones, generally meaning the class of "Hard Rocks") in alchemy, and was later used famously when describing experiments in a published paper by Antoine Lavoisier where such earths are mentioned as the source of his isolation of the element silicon in 1787. It is a little used term nowadays, primarily used to describe finely ground silicates used as pigments in paints.
Silex Process, a laser separation technique for uranium enrichment
Silex, a brand of "Proctor-Silex", a company making small appliances
Silex Innovations, a company that makes industrial engine exhaust systems.
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